Reactive dendrimers

ABSTRACT

A process for modifying at least one dendron that is intended to form part of a dendrimer is disclosed. One reacts at least one reactable unsaturated group in a chemoselective manner to form a less unsaturated group. Also disclosed is a process for modifying dendrimers in a similar manner.

This application claims priority on GB0220092.1 filed on Aug. 29, 2002and PCT/GB2003/003713 filed on Aug. 27, 2003.

This invention relates to a process for forming dendrons and dendrimersand their use in opto-electric devices.

BACKGROUND

Dendrimers are branched macromolecules with a core and attacheddendrons, also known as dendrites. Dendrons are branched structurescomprising branching units and optionally linking units. The generationof a dendron is defined by the number of sets of branching groups; seeFIG. 1. Dendrons with the same structure (architecture) but a highergeneration, or order, are composed of the same structural units(branching and linking units) but have an additional level of branching.There can be surface groups on the periphery or distal units of thedendrons.

Dendrimers of different generations can have different types ofbranching points and linking units. Dendrimers are generally synthesisedby convergent or divergent routes. Convergent routes require afunctional group at the dendron foci which can either be reacteddirectly to give a higher generation dendron or dendrimer or activatedbefore the reaction to form a higher generation dendron or dendrimer.For divergent routes the distal functional groups are used, either afteractivation or directly, to form the next higher generation dendrimer.Once the dendrimer is formed it has been demonstrated that the surfacegroups can be modified, e.g. t-butylcarbonates can be removed to leavehydroxyl moieties. The linking, branching, and core units of a dendrimercan either be made up of saturated or unsaturated units. The presence ofunsaturated units within a dendron or dendrimer gives rise to thepossibility of modifying the structure to form a final dendrimer thathas beneficial properties and which could not be formed easily byanother method. In particular this invention pertains to a chemicalconversion of one or more unsaturated units within a dendron ordendrimer to give bonds which are more saturated between the atomswithin the unit. The process is different from other reported reactionsof unsaturated units. For example it has previously been shown that whendi-substituted vinylene units are present within a dendrimer they can beisomerised (see J. N. G. Pillow et al, Macromolecules, 1999, 32, 5985).Although this is a chemical transformation it does not change the levelof saturation and therefore falls outside the scope of this invention.In addition, it has been reported that phenylene based dendrimers havebeen oxidised to form graphite like structures (FIG. 8A illustrates onecomponent of a dendrimer) (M. D. Watson et al, Chem. Rev., 2001, 101,1267). Although this is a reaction within the dendron and/or dendrimerstructure it does not constitute a reduction in the level of saturationof the sp² hybridised carbons of the benzene rings. In this case thecarbon-proton bond is merely converted to a carbon-carbon bond.Similarly di-dendroned substituted 4,4′-diphenylacetylene dendrons havebeen cyclised to form larger benzene centered dendrimers (M. D. Watsonet al, Chem. Rev., 2001, 101, 1267). The starting material in FIG. 8B isa dendron where the acetylene unit is the focus with two dendronsattached. The foci of three of these dendrons react to form the centralbenzene unit of the dendrimer and the other components of the dendronsare unchanged. Recently dendrimers that have unsaturated units have beenshown to be useful as the light emitting-layer in organic light-emittingdiodes.

Organic light-emitting diodes (OLEDs), also known as organicelectroluminescent (EL) devices, are an emerging display technology. Inessence an OLED comprises a thin organic layer or stack of organiclayers sandwiched between two electrodes, such that when a voltage isapplied visible or other light is emitted. At least one of theelectrodes must be transparent to light. For display applications thelight must of course be visible to the eye, and therefore at least oneof the electrodes must be transparent to visible light.

There are two principal techniques that can be used to deposit theorganic layers in an OLED: thermal evaporation and solution processing.Solution processing has the potential to be the lower cost technique dueto its potentially greater throughput and ability to handle largesubstrate sizes. Significant work has been undertaken to developappropriate materials, particularly polymers. More recently dendrimersthat are photoluminescent in the solid state have been shown to havegreat promise as solution processible light-emitting materials in OLEDs(S.-C. Lo, et al Adv. Mater., 2002, 13, 975; J. P. J., Markham, et alAppl. Phys. Lett., 2002, 80, 2645).

Light-emitting dendrimers typically have a luminescent core and in manycases an inherently at least partially conjugated dendrons. As usedherein, an inherently at least partially conjugated dendritic structureis one in which there is conjugation between the groups making up thedendritic structure, but the pi-system is not necessarily fullydelocalised. The delocalisation of the pi-system is dependent on theregiochemistry of the attachment of the different groups. Such dendronscan also be conjugated dendrons. Further examples of light-emittingdendrimers include those found in P. W. Wang, et al Adv. Mater., 1996,8, 237; M. Halim, et al Adv. Mater., 1999, 11, 371; A. W. Freeman, et alJ. Am. Chem. Soc., 2000, 122, 12385; A. Adronov, et al Chem. Comm.,2000, 1701; C. C. Kwok, et al Macromolecules, 2001, 34, 6821.Light-emitting dendrimers have the advantage over light-emittingpolymers that the light-emitting properties and the processingproperties can be independently optimised as the nature of the core,dendrons and surface groups can be independently altered. For examplewith dendrimers that contain light-emitting cores the emission colour ofthe dendrimer can be changed by simply changing the core. Althoughdendrimers with a light-emitting core are preferred, when the core isnot luminescent the chromophores in the dendron can be light-emitting.

Other physical properties, such as viscosity, may also make dendrimersmore easily tailored to the available manufacturing processes thanpolymers. Organometallic dendrimers have previously been used in OLEDapplications as a single component in a film (i.e. a neat film) or in ablend with a molecular material or in a blend of more than one dendrimerof different type (i.e. different cores), e.g. J. M. Lupton et al. Adv.Funct. Mater., 2001, 11, 287 and J. P. J., Markham, et al Appl. Phys.Lett., 2002, 80, 2645.

Intermolecular interactions play an important role in theopto-electronic properties of organic light-emitting and transportmaterials. Close contact and good order can lead to high chargemobilities but can also give rise to reduced emission due to theformation of excited-state dimers. In previous work we have shown thatintermolecular interactions can be controlled by the generation of thedendrons attached to a dendrimer (J. M. Lupton, et al Phys. Rev. B,2001, 63, 5206; J. P. J., Markham, et al Appl. Phys. Lett., 2002, 80,2645). However the nature of the intermolecular interactions is affectedby the type of dendron that is attached to the core. Generally, when thedendrimers are prepared via a convergent or divergent route the mainstructure of the final dendrimer is defined by the dendron branchinggroups and linking units used in the synthesis. This gives a limitationover the control of the dendrimer architecture and properties. Within adendron or dendrimer there is potential for the surface groups,branching groups and linking units, where present, and foci in the caseof dendrons, and core in the case of dendrimers, to be modified. It isknown that surface groups of dendrimers and dendrons and the foci ofdendrons can be modified. However, as many dendrimers contain saturatedlinking units and branching groups the modification of these units canbe difficult. In contrast dendrons or dendrimers containing unsaturatedunits within the linking units and branching groups of the dendrons andthe core offer an unexpected advantage for modifying the dendron anddendrimer structures. This is different from the reactions used in thedivergent or convergent route where a surface or focal group thatcontains unsaturation is converted into a surface group for furthergeneration building. For example, in a divergent route the surfacegroups of the lower generation are typically activated to make themreactive to the species added in the next stage. This is illustrated inthe synthesis of poly(iminopropane-1,3-diyl) (PPI) dendrimers which areformed by the Michael addition of acrylonitrile to 1,4-diaminobutane.After the addition the resultant terminal nitrile groups are reduced toform the primary amine terminated first generation dendrimer, which canthen be reacted with more equivalents of acrylonitrile. The reduction isrepeated to form the next generation dendrimer (Topics in CurrentChemistry, Dendrimers III, p 86, Springer-Verlag, Berlin Heidelberg,2001). This approach is different from that of the current invention, inwhich the entire dendron or dendrimer structure is built such that itcontains unsaturated units within the branching groups and/or linkingunits and/or core, and then the dendron or dendrimer is modified byreaction of some or all of said units. In particular unsaturated groupssuch as acetylenyl and vinyl groups within the dendron of a dendrimerare reacted. With this method we have been able to produce dendrimerswith aryl branching groups linked by ethylene units using the powerfulPd catalysed coupling of aryl halides and alkenes, followed by simplehydrogenation. In contrast, previous routes to saturated links betweenaromatic branching groups have involved a complex series of reactionswhere the hydrocarbon linking unit is introduced via a number of stepsprior to the Pd coupling to form the dendrimer (Z. Bo, A. D. Schlüter J.Org. Chem. 2002, 67, 5327). A further advantage of this invention isthat it gives additional flexibility in the choice of end product. Afterthe coupling to form the unsaturated unit a range of reactions, such ashalogenation and hydrogenation of alkenes and acetylenes can be used togive a variety of alternative products from the same intermediatematerial. We have discovered that by using dendrons that containacetylene and vinylene links between branching points in dendrons andfurther reacting them it gives a way of advantageously modifying thedendrons and hence the dendrimers.

SUMMARY OF THE CURRENT INVENTION

The present invention is thus directed at overcoming limitations in thesynthetic procedures for the formation of dendrons and dendrimers withsaturated units in the dendrons and/or core, and their use inopto-electronic devices, in particular OLEDs.

According to the present invention there is provided a process formodifying at least one dendron intended to form part of a dendrimer,said dendron having the formula:FO(dendrite−Q_(a))_(y)  (I)wherein FO is a functional group attached, either directly or via alinking group which can contain one or more reactable unsaturated units,to the first branching atom or group of the dendrite, each “dendrite”which may be the same or different is a dendrite which containsbranching atoms or groups and optionally linking groups and comprises atleast said first branching atom or group which must have, in addition toFO (either directly or via a linking group), 2 or more groups attachedand in which the distal group of each arm of the dendrite is an aryl orheteroaryl group, at least one of said dendrite or, if present, thelinking group to FO containing one or more reactable unsaturated units,y is 1 or more, Q is a surface group and a is 0 or an integer, whichcomprises reacting at least one said reactable unsaturated group in achemoselective manner to form a less unsaturated group.

When a is 0 there are no surface groups but preferably a is an integer,generally from 1 to 16.

The present invention also provides a process for modifying a dendrimerof the formula:CORE−[dendrite−Q_(a)]_(x)wherein Q and a are as defined above, x is one or 2 or more such thatwhen x is more than one each dendrite−Q_(a) can be the same or differentand CORE represents an atom or group and CORE terminates at the singlebond to the first branching atom or group in the or each dendrite, each“dendrite” which may be the same or different is a dendrite whichcontains branching atoms or groups and optionally linking groups, atleast one of CORE and “dendrite” comprising at least one reactableunsaturated group, provided that the distal group of each arm of the oreach dendrite is an aryl or heteroaryl group, which comprises reactingat least one reactable unsaturated group to form a less unsaturatedgroup in a chemoselective manner e.g. while leaving Q unchanged.

The present invention also provides a process for making a dendrimerwhich involves reacting at least one dendron with a dendrimer precursorwherein the dendron is one which has been modified by a process of thisinvention. Such a process can be carried out in conventional mannerwhereby the functional group, FO, of the dendron reacts with thedendrimer precursor. By “functional group” as used herein is meant agroup which is capable of reacting, either directly or after activation,with one or more other molecules, such that optionally after attachmentof one or more further dendrons, a dendrimer is formed via a convergentroute. In general FO and Q should be such that they can be reactedindependently; they will therefore not be the same. The functional groupof the dendron, FO, can, in the resulting dendrimer, form part of thecore. The functional group, FO, can be one of two types. In one case itis a simple functional group such as an alcohol, halide, aldehyde orboronic acid group which can react with other moieties to form adendrimer. In these cases the functional group may no longer be presentin the final dendrimer. For example, aldehyde-focused dendrons reactwith pyrrole to form a porphyrin core with dendrons attached. Thealdehyde itself is no longer present, but the carbon atom of thealdehyde forms part of the porphyrin core. Alternatively the functionalgroup can be a more complex group consisting of a number of componentse.g. one or more (hetero)aryl rings. If, for example, the core isorganometallic then the functional group can be a ligand which isreacted with a metal cation to form the dendrimer. In this case, in thereaction to form the dendrimer, the functional group becomes part of thecore but is still readily identifiable as the starting moiety. Forexample dendrons linked to a 2-phenylpyridine functional group reactwith an iridium cation to form iridium based dendritic complexes with2-phenylpyridine as part of the core. The functional group may requireactivation, e.g. deprotection or transformation into another type offunctional group, before it will react with the other molecule to form adendrimer. However, it is the functional group that is at the foci, andnot the link between FO and the first branching atom or group in thedendrite that is used to form the dendrimer. When FO is attached todendrite via a linking unit the backbone of the linking unit iscomprised of only sp and/or sp² hybridised atoms (before modification).The other reactive moieties that react with the dendrons to form thedendrimers, such as pyrrole or iridium trichloride in the examplesmentioned above, are viewed as dendrimer precursors. One or moredendrimer precursors may be involved in forming the dendrimer.

Particularly with an organometallic dendrimer, y can be more than one;for example with a bicyclic ligand such as phenyl-pyridyl a dendrite canbe attached to each ring.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows how the generation of a dendron is defined by the number ofsets of branching groups.

FIG. 2 shows that dendrons or dendrimers that can be considered formodification must contain at least one unsaturated group (the reactablegroup) within the dendron or dendrimer, which are not surface groups,and that can be further reacted.

FIG. 3 shows that a preferred dendron has either an acetylenyl or vinylunit at its foci which can be reacted with, or will become part of thecomponent of, the core wherein the unsaturated bond is reacted to form asaturated link hence disconnecting electronically the core chromophorefrom unsaturated units in the dendron.

FIG. 4 shows the Example 1 process of modification of stilbenecontaining dendrons by hydrogenation to form ethylene links between thebranching phenyl rings and their subsequent transformation toluminescent dendrimers containing porphyrin cores.

FIG. 5 shows the Example 2 process for the formation of a dendrimer withan iridium cation as part of its core and saturated units formed byhydrogenation of vinylene units.

FIG. 6 shows that a preferred dendron has either an acetylenyl or vinylunit at its foci which can be reacted with, or will become part of thecomponent of, the core wherein the unsaturated bond is reacted to form asaturated link hence disconnecting electronically the core chromophorefrom unsaturated units in the dendron.

FIG. 7 shows that including one or more unsaturated units in the dendronthen, after dendron or dendrimer formation, these units can be convertedto reactive groups which can be used in patterning or crosslinkingprocesses, and that preferably the unsaturated unit to be reacted isnear the distal end of the dendron or dendrimer.

FIG. 8A shows how phenylen based dendrimers can be oxidised to formgraphite like structures.

FIG. 8B shows how di-dendroned substituted 4,4-diphenylacetylenedendrons have been cyclised to form larger benzene centered dendrimers.

DETAILED DESCRIPTION OF THE CURRENT INVENTION

The present invention is directed towards modifying unsaturated groupsincluding vinylene, acetylenyl, imino, azo or vinylnitrile units withina dendrite or CORE either before reaction to form a dendrimer or as partof a dendrimer, the dendrimers that have been made by this process andthe subsequent use of these dendrimers in opto-electronic devices and inparticular OLEDs.

There are several types of dendrons or dendrimers that can be consideredfor modification but all must contain at least one unsaturated group(the reactable group) within the dendron or dendrimer, which are notsurface groups, and that can be further reacted (FIG. 2). Thesereactable groups, which can form a branching point as in the case of 6and 7 (see FIG. 2), are groups that are capable of undergoing reactionsto form more saturated and preferably fully saturated bonds between theatoms. For example, an acetylene bond could be reduced under Lindlar'sconditions to a vinylene or using hydrogen and palladium on charcoal toform an ethylene. A chemoselective reaction is one in which only thereactable unsaturated groups in the molecule undergo the reaction andthe other groups in the molecule, including FO (if present) and all Q,are unchanged by the reaction. The branching points of the dendrite caneither be an atom such as nitrogen or a group, but are preferably anaryl or heteroaryl where aryl and heteroaryl can also form part of afused ring system. More preferably the branching unit is a 1,3,5substituted benzene or 3,6,N-substituted carbazolyl group. Typically thereactive group is vinylene or acetylene and in a dendrimer either formsthe links between all branching groups of the dendrite or forms the partof the core directly bonded to the first branching point of the dendriteor is a link between the last branching group of the dendrite and thedistal, aryl, group of the dendrite. In one embodiment the, or each,dendrite in the dendron contains at least one reactable unsaturatedgroup. In a second embodiment the dendrite contains the only reactiveunsaturated group. In another embodiment the, or each, linking groupbetween FO and the first branching point of the dendrite contains theonly reactable unsaturated groups in the dendron. In a furtherembodiment, the CORE contains the only reactable unsaturated groups inthe dendrimer. The links between the branching points (BG in FIG. 2) canall be of one type, e.g. acetylenyl as in 1 in FIG. 2, vinyl as in 2, ora mixture as in 3. It is preferred that only non-aryl groups arereacted. For 1, 2, and 3 one or more of the unsaturated links can beconverted, depending on the number of equivalents of reagents, accordingto the process of this invention into a saturated link; this may giverise to a mixture of dendrons or dendrimers. It is preferred that allthe equivalent unsaturated groups are reacted. For example, if vinyleneunits are present then they are all reacted. In 4 the branching moietyhas two vinylene and one methylenoxy linking unit; the two alkene groupscan be converted. An alternative asymmetric dendrimer type is one havinga mixture of alkenyl, acetylenyl and aryl-aryl bonds in the dendrons. 5illustrates an example of the alkenyl and aryl case. It is preferredthat in this case only the alkenyl and acetylenyl groups react. One ofthe branching points can also be considered to be the unsaturated carbonatom as in the case of the vinylene 6 and imine 7 units. Preferably inthe case that all the links between the branch points are reactive theyare comprised of vinyl or acetylenyl or a combination of the two. Ingeneral the backbone of the linking group(s) is only comprised of spand/or sp² hybridised atoms. The combination of vinyl and acetylene witharyl and heteroaryl branches and aryl-aryl links of which 5 is anexample is also preferred. Preferred units include phenyl-vinyl-phenyland phenyl-acetylenyl-phenyl. It is especially preferred that thebranching group is (hetero)aryl which remains unchanged when unsaturatedgroups are reacted e.g. hydrogenated. It will be appreciated that therecan be different numbers and combinations of conjugated units betweenbranching points. The reaction of vinyl, acetylenyl or iminyl groups togive saturated units removes the conjugation and potentially introducesnew functionality. In a preferred embodiment the unsaturated groupbecomes fully saturated. In some cases the new functionality can befurther reacted, e.g. in cross-linking reactions. For example, additionof hydrogen bromide to a vinylene unit between two phenyl groups in thedendron would give rise to a benzylic bromide which could be substitutedby a range nucleophiles such as alcohols. Where a diol is used twodendrons or dendrimers could be covalently linked together. It will beappreciated that a linking unit may have more than one unsaturated unitcapable of reaction. For example, there may be a divinylbenzene linkbetween two phenyl branch points.

Examples of dendrons and dendrimers which can be subjected to theprocess of this invention include dendrimers which have at least oneinherently partially conjugated dendron such as those described inWO99/21935 for example those of formula (A):CORE−[DENDRITE]_(n)  (A)in which CORE represents an atom or group, n represents an integer of atleast 1 and DENDRITE, which may be the same or different if n is greaterthan 1, represents an inherently at least partly conjugated dendriticmolecular structure comprising aryl and/or heteroaryl groups and alkenylgroups connected to each other via a carbon atom of an alkenyl group toa ring carbon atom of an aryl or heteroaryl group, CORE terminating inthe first single bond which is connected to a ring carbon atom of an(hetero)aryl group to which more than one at least partly conjugateddendritic chain is attached, said ring carbon atom forming part ofDENDRITE, the CORE and/or DENDRITE being luminescent,including ones where the dendrons are not all the same as disclosed inPCT/GB02/00765, in general those having the formula (B):CORE−[DENDRITE¹]_(n)[DENDRITE²]_(m)  (B)in which CORE represents an atom or group, n and m, which may be thesame or different, each represent an integer of at least 1, eachDENDRITE¹, which may be the same or different when n is greater than 1,and each DENDRITE², which may be the same or different when m is greaterthan 1, represent dendritic structures, at least one of said structuresbeing fully conjugated and comprising aryl and/or heteroaryl groups and,optionally, vinyl and/or acetylenyl groups, connected via sp² or sphybridized carbon atoms of said (hetero)aryl, vinyl and acetylenylgroups, and at least one branching point and/or link between thebranching points in DENDRITE¹ being different from those in DENDRITE²,CORE terminating in the single bond which is connected to a sp²hybridized (ring) carbon atom of the first (hetero)aryl group to whichmore than one conjugated dendritic branch is attached, said ring carbonatom forming part of said fully conjugated DENDRITE¹ or DENDRITE² andCORE terminating at the single bond to the first branching point for theother of said DENDRITE¹ or DENDRITE², at least one of the CORE,DENDRITE¹ and DENDRITE² being luminescent, and those of formula (C):CORE−[DENDRITE]_(n)  (C)in which CORE represents an atom or group, n represents an integer of atleast 1, each DENDRITE, which may be the same or different, representsan inherently at least partially conjugated dendritic molecularstructure which comprises aryl and/or heteroaryl and, optionally, vinyland/or acetylenyl groups, connected via sp² or sp hybridized carbonatoms of said (hetero) aryl, vinyl and acetylenyl groups, and whereinthe links between adjacent branching points in said DENDRITE are not allthe same, CORE terminating in the single bond which is connected to asp² hybridized (ring) carbon atom of the first (hetero)aryl group towhich more than one dendritic branch is attached, said ring carbon atomforming part of said DENDRITE, the CORE and/or DENDRITE beingluminescent and ones where the dendrons comprise aryl-aryl ligands andbranching points as disclosed in PCT/GB02/00739, in general those havingthe formula (D):CORE−[DENDRITE(−Q)_(a)]_(n)  (D)in which the CORE represents an atom or group, n represents an integerof at least 1, Q is a proton or a surface group, a is an integer andDENDRITE, which may be the same or different if n is greater than 1,represents a conjugated dendritic structure comprising aryl and/orheteroaryl groups connected to each other via bonds between sp²hybridised ring atoms of said aryl or heteroaryl groups, COREterminating in the first single bond which is connected to an sp²hybridised ring atom of an (hetero)aryl group to which more than oneconjugated dendritic branch is attached, said atom forming part of theDENDRITE, the CORE and/or DENDRITE being luminescent as well asorganometallic dendrimers as disclosed in PCT/GB01/00750 typically thosehaving the formula (E):CORE−[DENDRITE]_(n)  (E)in which CORE represents a metal ion or a group containing a metal ion,n represents an integer of 1 or more, each DENDRITE, which may be thesame or different, represents an inherently at least partiallyconjugated dendritic molecular structure comprising aryl and/orheteroaryl groups or nitrogen and, optionally, vinyl or acetylenylgroups connected via sp² or sp hybridised carbon atoms of said(hetero)aryl vinyl and acetylenyl groups or via single bonds between Nand (hetero)aryl groups, CORE terminating in the single bond which isconnected to an sp² hybridised (ring) carbon atom of the first(hetero)aryl group or nitrogen to which more than one at least partiallyconjugated dendritic branch is attached, said ring carbon atom or Nforming part of said DENDRITE, and nitrogen-core containing dendrimersas disclosed in WO01/59030 in general those having the formula (F):

where x is 3, 2 or 1, n¹ and n², which may be the same or different, are0 or 1 to 3, X represents a divalent mono- or poly-aromatic and/orheteroaromatic moiety, the or each Y, which may be the same or differentif x is 1, represents hydrogen or an optionally substituted hydrocarbongroup, Z represents an inherently at least partly conjugated dendriticmolecular structure comprising aromatic and/or heteroaromatic groups andoptionally, alkenylene groups, connected to each other either via acarbon atom of a heteroaromatic group to a ring carbon atom of another(hetero)aromatic group or, if an alkenylene group is present via a ringcarbon atom of a (hetero)aromatic group to a carbon atom of analkenylene group, said dendritic molecular structure being connected tothe remainder of the molecule via a ring carbon atom of a(hetero)aromatic group to which more than one at least partly conjugateddendritic chain is attached, one or more of the (hetero)aromatic ringsof the dendrimer optionally being substituted, Z and/or the remainder ofthe molecule, excluding any groups Y, being luminescent, typically xmust be 3, to which reference should be made for further details. Itwill be appreciated that in the case of formula D it is preferred thatthe reactive unsaturated units are part of the CORE.

Whilst it is preferred that the dendrons and dendrimers formed aftermodification contain chromophores suitable for opto-electronicapplications and, in particular, light-emitting diodes the process ofthis invention can be used to prepare dendrimers suitable for otherapplications including dendrimers that have dendrons and/or corescomprised of the basic repeating units of linear polymers but in abranched form. For example, a dendrimer containing phenyl branchingpoints and vinylene linking units as described in WO99/21935 would, onceall vinylene units are saturated according to a process of thisinvention, give a dendritic version of poly(phenyleneethylene). Inparticular though dendrimers that contain luminescent cores and/ordendrons, and can be used in OLEDs, are preferred. The cores of thedendrimers can be fluorescent or phosphorescent. In the case offluorescent cores that are only comprised of organic units, i.e. nometal cations, aryl and heteroaryl and fused aryl and heteroaryl anddirectly linked aryl and heteroaryl systems are preferred. That is thecore should not contain unsaturated units that are not aromatic (sinceotherwise they may react when the non-aromatic unsaturated groups in thedendron are reacted). Examples include phenyl, fluorenyl, thiophenyl,pyridyl and substituted derivatives thereof. Although fluorescent metalcomplex cores are possible, phosphorescent metal complex cores arepreferred. Preferred metal cations that are part of the core areiridium, which is most preferred, rhenium, rhodium, and platinum withthe dendrons attached to aryl and nitrogen heteroaryl containing ligandsincluding, for example ligands containing two aromatic groups selectedfrom pyridine, phenyl, benzothiophene, pyrimidinyl, pyrazinylpyridazinyl, imidazolyl, quinolinyl, isoquinolinyl, naphthyl, anthryl,phenanthryl, benzamidoazolyl, carbazolyl, fluorenyl, pyrazolinyl,oxazolinyl, oxadiazolinyl, triazolyl, triazinyl, thiadiazolyl,benzimidazolyl, benzoxazolyl, furyl, and in particular phenyl-pyridyland substituted derivatives.

The surface groups of the dendrimers are generally selected so that thedendrimer is soluble in solvents suitable for solution processing, e.g.THF, toluene, chloroform, chlorobenzene, xylenes and alcoholic solventssuch as methanol. Suitable groups include those disclosed in WO99/21935.The surface groups can also be chosen such that the dendrimer can bepatterned. For example, a cross-linkable group can be chosen, which canbe crosslinked upon irradiation or by chemical reaction, as a surfacegroup. Alternatively, the surface groups can comprise protecting groupsthat can be removed to leave crosslinkable groups. In the case offurther reactive surface groups they should be chosen so that they willbe stable under the conditions used to react the unsaturated bondswithin the dendron or dendrimer. Therefore, vinyl surface groups shouldgenerally not be present. The distal groups of the dendrite, to whichthe surface groups are attached, are aryl or heteroaryl groups. Wheret-butyl groups are the surface groups attached to phenyl rings it ispreferable that more than one is attached to each of the distal phenylunits.

In a particular embodiment the initial dendrimer is an organometallicdendrimer with a metal cation as part of its core and with at least onedendron which comprises at least one nitrogen atom which forms part ofan aromatic ring system or is directly bonded to at least two aromaticgroups of the type described in our GB application No. 0206356.8 wherethe dendron is connected via a vinylene or acetylenyl group of the core.The vinylene or acetylenyl group is then converted into an ethylenegroup.

In one embodiment the dendrimer is not of the formula:

generally having been obtained by hydrogenating a dendron of theformula:

where R is 2-ethylhexyloxy.

Especially the dendron takes the structure

wherein Y is oxygen in which case -Z₁-Z₂- represents —N═CR¹—, or Y is—N—R² in which case -Z₁-Z₂ forms part of a benzene ring or —N═CR¹, R¹represents an optionally substituted benzene radical and R² representsan optionally substituted alkyl or aryl group. Thus thenitrogen-containing rings are either oxadiazoles or imidazoles ortriazoles. Thus the reaction is typically as shown in FIG. 6. R¹ istypically substituted by one or more surface groups, e.g.3,5-di-tertiary butyl. R² is phenyl, which is preferred, or alkyl, forexample of 1 to 15 carbon atoms such as methyl or ethyl; these can besubstituted, for example when R² is phenyl then it can be substitutedwith, for example, one or more alkyl, alkoxy or halo substituents. Thesedendrimers form another aspect of the present invention.

The present invention also provides an organometallic dendrimer with ametal cation as part of its core wherein the core is attached directlyto the first branching group of at least one dendron by an ethylene orsubstituted ethylene group.

There are many reactions known in the art that can be carried out onunsaturated bonds; the only restriction is that they must bechemoselective, that is only react with the desired functional group(s).For example, whilst vinylene units can be hydrogenated to give ethyleneunits, hydrogenation can also be used to cleave benzyl ethers.Therefore, in the case of 4 when the branching group BG is phenyl,hydrogenation has to be carried out so as to react the vinyl (which arethe more reactive groups) but not the benzyl ethers. Examples of usefulreactions are hydrogenation of vinylene and acetylenyl groups which willgive ethylene groups, and the reduction of imines to give amines. It canalso be an addition reaction. Vinylenes and acetylenes can also bereacted to give difluoro and tetrafluoro ethylenes. Reaction ofvinylenes with diborane (hydroboration) followed by an oxidative work-upcan lead to alcohols. The reaction of vinylenes with HSiCl₃ in thepresence of H₂PtCl₆ can give trichloroalkyl silanes (hydrosilylation)which can be further reacted. Vinylenes may also undergo electrophilicaddition reactions with hydrogen halides (hydrohalogenation) (HX, e.g.H═Cl or Br) or dihalogens (halogenation)(X₂) giving monohaloethylenesand dihaloethylenes respectively, while acetylenes will givedihaloethylenes and tetrahaloethylenes. Unsaturated units such asacetylene and vinylene can also undergo cycloaddition reactions althoughthese are less preferred. For example, Diels-Alder reactions and1,3-dipolar cycloadditions can be used providing that the unsaturatedgroup that has been reacted has less unsaturation between the atomsinvolved in the original bond than it did before the reaction. All thesereactions are well known and those skilled in the art will be well awareof the reaction conditions to employ, in particular if it is desired tobe chemoselective.

Another advantage of this invention is that not all surface groups whichare suitable for synthesis and initial processing are compatible withthe chemistry to form the dendrons and/or dendrimers and still beavailable for cross-linking and patterning processes. By including oneor more unsaturated units in the dendron then, after dendron ordendrimer formation, these units can be converted to reactive groupswhich can be used in patterning or crosslinking processes. For thisaspect of the invention it is preferable that the unsaturated unit to bereacted is near the distal end of the dendron or dendrimer, as shown inFIG. 7.

A preferred dendron has either an acetylenyl or vinyl unit at its fociwhich can be reacted with, or will become part of the component of, thecore. This unsaturated bond is then reacted to form a saturated linkhence disconnecting electronically the core chromophore from unsaturatedunits in the dendron, as shown in FIGS. 3 and 6. This can give enhancedcontrol of the colour purity of core emission and can enable theformation of dendrimers which could not be easily synthesisedotherwise,—see e.g. FIG. 6.

The properties of dendrimers make them ideal for solution processing.Preferred dendrimers can be dissolved in a solvent, the solutiondeposited onto a substrate, the solvent removed to leave a solid film.Conventional solution-processing techniques can be used, for examplespin-coating, printing (e.g. ink-jet printing) and dip-coating. Theresulting solid film is preferably formed on one side of a substrate;the thickness of the solid film is preferably no greater than 2 microns.

The present invention also provides an OLED incorporating a solid filmcomprising one or more of the dendrimers obtained by the process of thisinvention. In its simplest form, an organic light-emitting orelectroluminescent device can be formed from a light-emitting layersandwiched between two electrodes, at least one of which is transparentto the emitted light. More commonly there is one or morehole-transporting layers between the anode and the light-emitting layerand/or one or more electron-transporting layers between thelight-emitting layer and the cathode.

The present invention then also provides an OLED device comprisinglayers, in sequence of a substrate, an electrode, a first optionalcharge-transporting layer, an emissive layer, a second optionalcharge-transporting layer and a counter electrode, wherein one of theemissive layer or the first or second charge-transporting layers, ifpresent, especially the emissive layer, comprises at least in part of adendrimer obtained by the process of this invention.

In one embodiment a device according to the invention comprises, atleast in part, a dendrimer with a modified dendron and/or core andcontains one or more additional species, such as light-emitting dopants,charge-transporting species and/or additional molecular, dendriticand/or polymeric materials.

In one preferred embodiment the film comprising the dendrimer forms thelight-emitting layer in an OLED. It is particularly preferred that thedendrimers are the light-emitting species in this light-emitting layer.In an alternative embodiment the film comprising the dendrimer forms acharge-transporting layer in an OLED.

Such a device can have a conventional arrangement comprising atransparent substrate layer, e.g. a glass or PET layer, a transparentelectrode layer, a light-emitting layer and a second electrode. Theanode, which is generally transparent, is preferably made from indiumtin oxide (ITO) although other similar materials including indiumoxide/tin oxide, tin oxide/antimony, zinc oxide/aluminium, gold andplatinum can also be used, as can conducting polymers such as PANI(polyaniline) or PEDOT/PSS. The cathode is normally made of a low workfunction metal or alloy such as Al, Ca, Mg, Li or MgAl or optionallywith an additional layer of LiF. In an alternative configuration, thesubstrate may be made of an opaque material such as silicon and light isemitted through the opposing electrode. The OLED devices may be activelyor passively addressed.

For a typical OLED device, as described above where the dendrimer isemissive, a solution of the dendrimer can be applied over a transparentelectrode layer, the solvent evaporated and then subsequentcharge-transporting layers can be applied. The thickness of thedendrimer layer in the OLED is typically 10 nm to 1000 nm, preferably nomore than 200 nm, more preferably 30 nm to 120 nm. When a hole transportlayer is incorporated between the anode and the emissive dendrimercontaining layer the hole transport material must not be removed to asignificant extent during the solution deposition.

An OLED device incorporating an emissive layer comprising the dendrimermay optionally have an adjacent first and/or second charge-transportinglayer. In our work on dendrimers, it has been found that it isparticularly beneficial to have at least onehole-blocking/electron-transporting layer between the light-emittingdendrimer layer and the cathode. Suitable materials for such ahole-blocking/electron-transporting layer are known and include2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP),1,3,5-tris[2-N-phenylbenzimidazolyl)benzene (TPBI), and2-biphenyl-5(4′-t-butylphenyl)oxadiazole (PBD) aluminiumtris(8-hydroxyquinolate) (Alq) and aluminiumbis(2-methyl-8-quinolato)-4-phenylphenolate (BAlq). In this, and inother embodiments, the dendrimer-comprising layers may comprise mixturesof two or more dendrimer types, not all of which need be dendrimers ofthis invention.

Furthermore, additional emissive (fluorescent or phosphorescent) orcharge-transporting species may optionally be added to the layer of thedendrimers to improve device characteristics, e.g. efficiency andlifetime. It may further be of benefit to include one or more othermolecular and/or dendrimeric and/or polymeric species in the dendrimersto give improved performance. It is preferred that the molecular,dendritic or polymeric species can transport charge in its own right,for example a conjugated polymer or conjugated dendrimer. In oneembodiment such additional components form a part of the total blendfrom 95 to 5 mol %. For example, additional charge-transportingcomponents for use with the light-emitting dendrimers are TPBI, PBD,BCP, 4,4′-bis-(N-carbazolebiphenyl (CBP),4,4′,4″-tris(N-carbazolyl)triphenylamine (TCTA), andtris-4-(N-3-methylphenyl-N-phenyl) phenylamine (MTDATA).

Such dendrimers can also be used in other device applications such asphotovoltaic cells which can contain one or more layers. When used inphotovoltaic cells the dendrimer must be capable of absorbing lightand/or transporting charge. The dendrimer may be used as a homogeneouslayer in a photovoltaic device or blended with other molecular and/ordendritic and/or polymeric materials. Dendrimers may be used in one ormore layers of the photovoltaic device. In photovoltaic applications theorganometallic dendrimers need not necessarily be charge-neutral.

The Examples that follow further illustrate the present invention.

Example 1

This is illustrated in FIG. 4.

Example 1 describes the process of modification of stilbene containingdendrons by hydrogenation to form ethylene links between the branchingphenyl rings and their subsequent transformation to luminescentdendrimers containing porphyrin cores. Example 1 also illustrates thebenefit of carrying out the transformation by comparing thephotoluminescent quantum yields (PLQY) of dendrimers with porphyrincores with stilbene and diphenylethane based dendrons (see Table 1).

3,5-Bis[2-(3,5-di-tert-butylphenyl)ethyl)benzaldehyde 15

Hydroxylamine hydrochloride (77.66 g, 1.117 mol) was dissolved inN,N-dimethylformamide (216 cm³). Powdered potassium hydroxide (73.45 g,1.309 mol) was added and the solution stirred for 10 min, evolving heatand giving a white precipitate. The suspension was filtered, the solidwashed with N,N-dimethylformamide (40 cm³) and the filtrates combinedand cooled to 0° C. Ethyl acetate (48.6 cm³) was added to give a stocksolution which was stirred at 0° C. A suspension of3,5-bis(3,5-di-tert-butylphenyl-E-vinyl)benzyl alcohol 13 (1.00 g, 1.86mmol) and stock solution (20 cm³) was heated to 100° C. Stock solutionwas added in 20 cm³ portions at 20 min intervals with heating maintainedat 100° C., and the mixture, which had turned into a homogeneoussolution, heated to 100° C. for a further 1 h then allowed to cool.Water (100 cm³) was added and the product extracted into ether (2×100cm³). The extracts were washed with aqueous hydrochloric acid (3 M, 2×75cm³) and brine (75 cm³), dried over anhydrous magnesium sulphate,filtered and the solvent removed. The residue was purified by columnchromatography over silica with dichloromethane as eluent to leave3,5-bis[2-(3,5-di-tert-butylphenyl)ethyl)benzylalcohol (957 mg, 95%) asa white solid, mp 101° C. (Found: C, 86.7; H, 10.4. C₃₉H₅₆O requires C,86.6; H, 10.4%); ν_(max) (KBr)/cm⁻¹ 3401 (OH) and 1600 (C═C);λ_(max)(CH₂Cl₂)/nm 265 (log(ε/dm³mol⁻¹cm⁻¹) 2.95), 269 sh (2.93), 305(2.57), 317 (2.56) and 330 sh (3.37); δ_(H)(400 MHz, CDCl₃) 1.34 (36H,s, t-butyl), 1.57 (1H, s, OH), 2.92 (8H, s, CH₂CH₂), 4.68 (2H, d, J 6,CH₂OH), 7.03 (1H, s, bp-H), 7.07 (4H, d, J 2, sp-H), 7.09 (2H, d, J 1,bp-H) and 7.29 (2H, dd, J 2, sp-H); δ_(C)(100.6 MHz, CDCl₃) 31.5, 34.8,38.3, 38.7, 65.5, 119.9, 122.6, 124.7, 128.1, 140.85, 140.90, 142.6 and150.7; m/z (APCI⁺) 523.4 ((M-OH)⁺, 100%) and 558.4 (MNH₄ ⁺, 54%). Asolution of 3,5-bis[2-(3,5-di-tert-butylphenyl)ethyl)benzyl alcohol (914mg, 1.69 mmol) and pyridinium chlorochromate (729 mg, 3.38 mmol) indichloromethane (4 cm³) was stirred at room temperature for 18 h, thesolvent was removed and the residue purified by column chromatographyover silica with dichloromethane-light petroleum (2:3) as eluent toleave 15 (902 mg, 99%) as a viscous oil, mp 74-75° C. (Found: C, 86.8;H, 10.1. C₃₉H₅₄O requires C, 86.9; H, 10.1%); ν_(max)(KBr)/cm⁻¹ 1702(C═O) and 1599 (C═C); λ_(max)(CH₂Cl₂)/nm 258 (log(ε/dm³ mol⁻¹cm⁻¹) 4.18)and 300 (3.45); δ_(H)(400 MHz, CDCl₃) 1.38 (36H, s, t-butyl), 2.95 (8H,m, CH₂CH₂), 7.03 (4H, d, J 2, sp-H), 7.25 (1H, s, bp-H), 7.30 (2H, dd, J2, sp-H), 7.57 (2H, s, J 1.5, bp-H) and 9.98 (1H, s, CHO); δ_(C)(100.6MHz, CDCl₃) 31.5, 34.8, 37.9, 38.4, 120.1, 122.7, 127.5, 135.3, 136.7,140.2, 143.0, 150.8 and 192.8; m/z (EI⁺) 538.3 (M⁺, 18%).

3,5-Bis(2-{3,5-bis[2-(3,5-di-tert-butylphenyl)ethyl]phenyl}ethyl)benzaldehyde16

A solution of aqueous hydroxylamine (50% w/w, 65.6 cm³, inN,N-dimethylformamide (250 cm³) was cooled over a NaCl—ice bath. Ethylacetate (46.5 cm³, 0.475 mol) was added and the solution stirred below0° C. A 25 cm³ portion of this solution was added to a suspension of3,5-bis[3,5-bis(3,5-di-tert-butylphenyl-E-vinyl)phenyl-E-vinyl]benzylalcohol (2.09 g, 1.78 mmol) in toluene (42 cm³) and the mixture heatedto 100° C. A homogeneous solution had formed after a few minutes. Theremaining hydroxylamine solution was added portionwise over 3 h withstirring maintained at 100° C., and continued at 100° C. for a further 2h after the addition was complete. The solution was allowed to coolovernight. Water (150 cm³) was added and the mixture extracted withether (2×150 cm³). The combined extracts were washed with aqueoushydrochloric acid (3 M, 150 cm³), water (150 cm³) and brine (150 cm³),dried over anhydrous magnesium sulphate, filtered and the solventremoved. Analysis of the residue by ¹H NMR indicated incompletereduction of the vinyl bonds had occurred. The residue was thereforesubjected to the same reaction conditions as above but without thetoluene, in the place of the alcohol, to give, upon solvent removal,3,5-bis(2-{3,5-bis[2-(3,5-di-tert-butylphenyl)ethyl]phenyl}ethyl)benzylalcohol as a white solid foam (2.105 g, 100%), (Found: C, 88.0; H, 10.3.C₈₇H₁₂₀O requires C, 88.4; H, 10.2%); ν_(max)(KBr)/cm⁻¹ 1600 (C═C);λ_(max)(CH₂Cl₂)/nm 265 (log(ε/dm³ mol⁻¹cm⁻¹) 3.38), 269 sh (3.36), 306(3.08), 317 (3.08), and 332 sh (2.87); δ_(H)(400 MHz, CDCl₃) 1.35 (72H,s, t-butyl), 1.61 (1H, t, J 6 CH₂OH), 2.91 (24H, s, CH₂CH₂), 4.70 (2H,d, J 6, CH₂OH), 6.97 (6H, s, G1 bp-H), 7.09 (9H, m, sp-H and cp-H), 7.12(2H, s, cp-H) and 7.30 (4H, dd, J 2, sp-H); m/z (MALDI) 1204.9 (MNa⁺,100%). A solution of3,5-bis(2-{3,5-bis[2-(3,5-di-tert-butylphenyl)ethyl]phenyl}ethyl)benzylalcohol (1.317 g, 1.114 mmol) and pyridinium chlorochromate (0.480 g,2.23 mmol) in dichloromethane (20 cm³) was heated to reflux for 1 h andallowed to cool overnight. The dark brown slurry was then filteredthrough a plug of silica with dichloromethane as eluent to give 16 (1.29g, 98%) as a white solid foam, (Found: C, 88.3; H, 10.1. C₈₇H₁₁₈Orequires C, 88.6; H, 10.1%); ν_(max)(KBr)/cm⁻¹ 1701 (C═O) and 1600(C═C); λ_(max)(CH₂Cl₂)/nm 257 (log(ε/dm³mol⁻¹cm⁻¹) 4.12) and 300 (3.43);δ_(H)(400 MHz, CDCl₃) 1.35 (72H, s, t-butyl), 2.90-2.99 (24H, m,CH₂CH₂), 6.94 (4H, d, J 1, bp-H), 6.97 (2H, s, bp-H), 7.08 (8H, d, J 2,sp-H), 7.30 (4H, dd, J 2, sp-H), 7.36 (1H, s, cp-H), 7.61 (2H, d, J 1.5,cp-H) and 10.01 (1H, s, CHO); m/z (MALDI) 1202.2 (MNa⁺, 100%).

5,10,15,20-Tetrakis{3,5-bis[2-(3,5-di-tert-butylphenyl)ethyl)phenyl}porphyrin17

A solution of 15 (774 mg, 1.44 mmol), pyrrole (99.7 μl, 1.44 mmol) andtrifluoroacetic acid (111 μl, 1.44 mmol) in dichloromethane (111 cm³)was stirred in the dark under nitrogen for 9 days 2.5 h.2,3-Dichloro-5,6-dicyanobenzoquinone (326 mg, 1.44 mmol) was added andthe reaction stirred for 20 min, then neutralised by the addition of anexcess of sodium bicarbonate (ca. 1.0 g) and filtered through a plug ofsilica with dichloromethane as eluent. The residue was purified bycolumn chromatography over silica eluting with dichloromethane-lightpetroleum (1:2), collecting the main band 17 (231 mg, 28%) as a purplesolid, mp 215-217° C. (Found: C, 88.0; H, 9.5; N, 2.4; C₁₇₂H₂₂₂N₄requires C, 88.1; H, 9.5; N, 2.4%); ν_(max)(KBr)/cm⁻¹ 3316 (NH) and 1598(C═C); λ_(max)(CH₂Cl₂)/nm 301 (log(ε/dm³mol⁻¹cm⁻¹) 4.23), 374 sh (4.38),421 (5.81), 517 (4.31), 553 (4.03), 592 (3.80) and 647 (3.76); δ_(H)(400MHz, CDCl₃)-2.77 (2H, s, NH), 1.32 (144H, s, t-butyl), 3.18 (32H, m,CH₂CH₂), 7.16 (16H, d, J 1.5, so H), 7.31 (8H, dd, J 1.5, sp-H), 7.47(4H, s, bp-H), 7.93 (8H, d, J 1.5, bp-H) and 8.77 (8H, s, β-pyrrolic);m/z (MALDI) 2345.8 (M⁺, 100%).

5,10,15,20-Tetrakis[3,5-bis(2-{3,5-bis[2-(3,5-di-tert-butylphenyl)ethyl]phenyl}ethyl)-phenyl]porphyrin18

A solution of 16 (1.22 g, 1.03 mmol), pyrrole (71.5 μl, 1.03 mmol),trifluoroacetic acid (80 μl, 1.0 mmol) and dichloromethane (80 cm³) wasstirred under argon in the dark for 6 days 19 h.2,3-Dichloro-5,6-dicyanobenzoquinone (234 mg, 1.03 mmol) was added andthe reaction stirred for 5 min, then neutralised by the addition ofdiethylamine (2 cm³), filtered through a plug of silica withdichloromethane as eluent and the solvent removed. The residue waspurified by column chromatography over silica with dichloromethane-lightpetroleum as eluent. The product was precipitated from a dichloromethanesolution by the addition of methanol and dried under vacuum to leave 18(207 mg, 16%) as a foamy purple solid, (Found: C, 88.5; H, 9.5; N, 1.2.C₃₆₄H₄₇₈N₄ requires C, 89.1; H, 9.8; N, 1.1%); ν_(max)(KBr)/cm⁻¹ 1599(C═C); λ_(max)(CH₂Cl₂)/nm 302 (log(ε/dm³mol⁻¹cm⁻¹) 4.40), 373 (4.50),421 (5.80), 517 (4.35), 551 (4.14), 5.93 (3.83) and 651 (4.16);δ_(H)(400 MHz, CDCl₃)-2.64 (2H, s, NH), 1.26 (288H, s, t-butyl), 2.88(64H, s, G2 ethyl H), 3.13 (32, m, G1 ethyl H), 6.94 (8H, s, bp-H), 7.02(48H, m, sp-H bp-H), 7.22 (16H, dd, J 1.5, sp-H), 7.51 (4H, s, cp-H),8.04 (8H, d, J 2, cp-H) and 8.98 (8H, s, β-pyrrolic); m/z (MALDI) 4910.9(M⁺, 100%).

5,10,15,20-Tetrakis{3,5-bis[2-(3,5-di-tert-butylphenyl)ethyl)phenyl}porphinatoplatinum (II) 17a

5,10,15,20-Tetrakis{3,5-bis[2-(3,5-di-tert-butylphenyl)ethyl)phenyl}porphine 17 (150 mg,63.9 μmol) was added to a refluxing solution of platinum (II) chloride(34.0 mg, 0.128 mmol) in benzonitrile (2 cm³), washing in withbenzonitrile (1.0 cm³) and the mixture heated to reflux under nitrogenfor 21 h. The benzonitrile was removed and the residue was purified bycolumn chromatography over silica with dichloromethane-light petroleum(2:3) as eluent and the orange solid recrystallised from adichloromethane-methanol mixture to give 17a (143 mg, 88%) as orangecrystals, mp 128° C. (Found: C, 81.3; H, 8.7; N, 2.2. C₁₇₂H₂₂₀N₄Ptrequires C, 81.4; H, 8.7; N, 2.2%); ν_(max)(KBr)/cm⁻¹ 1598 (C═C);λ_(max)(CH₂Cl₂)/nm 293 (log(ε/dm³mol⁻¹cm⁻¹) 3.99), 405 (5.68), 511(4.60) and 540 (3.79); δ_(H)(400 MHz, CDCl₃) 1.32 (144H, s, t-butyl),3.15 (32H, m, ethyl H), 7.15 (16H, d, J 2, sp H), 7.31 (8H, dd, J 2, spH), 7.45 (4H, s, bp H), 7.87 (8H, d, J 1.5, bp H) and 8.68 (8H, s,β-pyrrolic H); m/z (MALDI) 2537.7 (M⁺, 100%).

5,10,15,20-Tetrakis[3,5-bis(2-{3,5-bis[2-(3,5-di-tert-butylphenyl)ethyl]phenyl}ethyl)phenyl]porphyrinatoplatinum (II) 18a

5,10,15,20-Tetrakis[3,5-bis(2-{3,5-bis[2-(3,5-di-tert-butylphenyl)ethyl]phenyl}-ethyl)phenyl]porphine18 (273 mg, 0.056 mmol) was added to a refluxing solution of platinum(II) chloride (54.0 mg, 0.203 mmol) in benzonitrile (1 cm³) and thesolution heated to reflux under a fast stream of nitrogen for 3.5 h. Thebenzonitrile was removed and the residue purified by columnchromatography over silica with dichloromethane-light petroleum (1:4) aseluent to leave 18a (213 mg, 75%) as an orange solid, mp 92-93° C.(Found: C, 84.5; H, 9.9; N, 1.18. C₃₆₄H₄₇₆N₄Pt requires C, 85.7; H, 9.4;N, 1.1%); ν_(max)(KBr)/cm⁻¹ 1599 (C═C); λ_(max)(CH₂Cl₂)/nm 295(log(ε/dm³mol⁻¹cm⁻¹) 4.32), 405 (5.53), 511 (4.47) and 540 (3.45);δ_(H)(400 MHz, CDCl₃) 1.26 (288H, s, t-butyl), 2.88 (64H, s, G2 ethylH), 3.13 (32, m, G1 ethyl H), 6.93 (8H, s, bp H), 7.02 (48H, m, sp H andG2-bp H), 7.23 (16H, dd, J 1.5, sp H), 7.49 (4H, s, G1-bp H), 7.98 (8H,d, J 1, G1-bp H) and 8.89 (8H, s, β-pyrrolic H); m/z (MALDI) 5103.8(MH⁺, 100%).

The PLQY of the free-base and platinum chelated porphyrins with thedendrons containing the unsaturated vinylene bonds between the phenylbranching points (stilbene) and equivalent dendrimers but with thevinylene units converted to saturated ethylene units were measured andthe results are shown in Table 1.

TABLE 1 Saturated Stilbene Film PLQY in Film PLQY in PLQY Compound THF(%) PLQY (%) Compound THF (%) (%) 22 12 1.7 17 13 0.8 23 10 1.8 18 114.8 22a 9 0.84 17a 16 2.2 23a 4 0.91 18a 16 2.6

Luminescence efficiency was generally enhanced upon hydrogenation of thestilbenes. For the vinylene porphyrins 22 and 23, the film PLQY was lessthan 20% of the solution PLQY. By hydrogenation to give dendrimer 18,the film PLQY was improved to 44% of the solution PLQY. In 17 the lower(first) generation dendrons do not give as good an isolation of thecore, so the film PLQY is still low. For the platinum porphyrin stilbenedendrimers 22a and 23a, the solution PLQY was low and decreased withincreasing generation. For the platinum porphyrin dendrimers 17a and 18awith ethylene links in the dendrons, the solution PLQY were higher anddid not decrease with increasing generation. The film PLQY for 17a and18a was also three times higher than that for 22a and 23a showing theimprovement in PLQY on removing the unsaturation in the dendrons.

Example 2

This is illustrated in FIG. 5 and shows the process for the formation ofa dendrimer with an iridium cation as part of its core and saturatedunits formed by hydrogenation of vinylene units.

2-(2′,4′-difluorophenyl)-5-[3″,5″-bis(3′″,5′″-di-tert-butylstyryl)styryl]pyridine20

A mixture of 3,5-bis(3′,5′-di-tert-butylstyryl)styrene 19 (2.161 g, 4.06mmol), 2-(2′,4′-difluorophenyl)-5-bromopyridine 9 (997 mg, 3.69 mmol),sodium carbonate (430 mg, 4.06 mmol), di-tert-butylcresol (407 mg, 1.85mmol), trans-di(μ-acetato)-bis[o-(di-o-tolylphosphino)benzyl]dipalladium(II) (174 mg, 0.185 mmol) and N,N-dimethylacetamide (50 cm³) wasdeoxygenated by alternate exposure to high vacuum and argon, then heatedat 130° C. for 21 hours. Water (100 cm³) and dichloromethane (100 cm³)were added. The aqueous layer was separated and extracted withdichloromethane (3×50 cm³). The combined organic layers were washed withwater (5×200 cm³), brine (200 cm³), dried over magnesium sulfate and thesolvent removed. The crude product was purified by column chromatographyover silica using ethyl acetate/light petroleum (1:8) as the eluent. Themain band was isolated and the solvent completely removed to give anorange oil. This was recrystallized from dichloromethane/methanol toleave an orange solid of 20 (810 mg, 30%), mp 230-233° C., found722.4540. C₅₁H₅₈NF₂ requires 722.4537; ν_(max)(Nujol)/cm⁻¹ 1594 (C═C);δ_(H)(400 MHz, CDCl₃) 1.39 (36H, s, t-Bu), 6.95 (1H, m, 6′-H), 7.04 (1H,m, 5′-H), 7.21 (1H, s, 4-H), 7.27 (2H, s, 8′″-H), 7.28 (2H, s, 7′″-H),7.33 (1H, s, 3-H), 7.41 (2H, t, J 1.7, 4′″-H), 7.45 (4H, d, J 1.7, 2′″,6′″-H), 7.64 (2H, d, J 1.1, 2″, 6″-H), 7.68 (1H, s, 4″-H), 7.82 (1H, dd,J 6, J′ 1.1, 7″-H), 7.97 (1H, dd, J 6, J′ 2, 8″-H), 8.09 (1H, td, J 11,J 8, 3′-H), 8.87 (1H, d, J 2, 6-H); m/z (APCI⁺) 720 (MH⁺, 100%).

2-(2′,4′-difluorophenyl)-5-[2″-(3′″,5′″-bis[2″″-(3″″′,5″″′-di-tert-butylphenyl)ethyl]phenyl)ethyl]pyridine21

A mixture of 20 (668 mg, 0.925 mmol), 5% palladium on carbon (100 mg,0.046 mmol) and tetrahydrofuran was deoxygenated and stirred underhydrogen (1 atm) for 17 hours. The mixture was filtered through Celite®using ether as eluent, and the solvent was removed to leave a brown oil.The crude product was purified by column chromatography over silicausing ethyl acetate-light petroleum (1:15) as the eluent. The main bandwas isolated and the solvent completely removed to give 21 (550 mg, 82%)as a pale oil, MH⁺ found 728.5007; C₅₁H₆₄NF₂ requires 728.5007;δ_(H)(400 MHz, CDCl₃) 1.34 (36H, s, t-Bu), 2.89 (8H, s, CH₂), 2.9-3.0(4H, m, CH₂), 6.85-7.05 (5H, m, 5′, 6′, 2″, 4″, 6″-H), 7.06 (4H, d, J1.8, 2′″, 6′″-H), 7.29 (2H, t, J 1.7, 4′″-H), 7.54 (11H, dd, J 8, J′2.2, 4-H), 7.58 (1H, dd, J 8, J′ 2.2, 3-H), 7.99 (1H, td, J 11, J 8,3′-H), 8.55 (1H, d, J 1.8, 6-H); m/z (APCI⁺) 728 (MH⁺, 100%).

Tris[3,5-difluoro-2-(5′-[2″-(3′″,5″′-bis[2″″-(3″″′,5″″′-di-tert-butylphenyl)ethyl]phenyl)ethyl]pyridinyl)phenyl-C,N]-iridium22

A mixture of 21 (177 mg, 0.24 mmol), iridium trichloride trihydrate (34mg, 0.097 mmol), water (1 cm³) and ethoxyethanol (3 cm³) was degassed,then stirred and heated at reflux under argon for 18 hours. Water wasadded until a yellow precipitate formed. This was filtered off,dissolved in dichloromethane, filtered and the solvent removed to leavea yellow solid. The crude product was passed through a plug of silicausing ethyl acetate-light petroleum (1:8) as the eluent to removebaseline impurities, to leave a yellow solid (130 mg). A mixture of theyellow solid (122 mg), 21 (280 mg, 0.385 mmol) and silver triflate (9mg, 0.0363 mmol) was heated at 150° C. under argon for 24 hours. Thecrude mixture was separated by column chromatography over silica usingdichloromethane-light petroleum (1:4) as the eluent to give 22 (40 mg,23%), yellow solid, mp 86-92° C.; δ_(max)(CH₂Cl₂)/nm 276(log(ε/dm³mol⁻¹cm⁻¹) 4.67), 346 (4.09), 381 sh (3.85); δ_(H)(400 MHz,CDCl₃) 1.28 (108H, s, t-Bu), 2.6-2.7 (12H, m, CH₂), 2.80 (24H, s, CH₂),6.28 (3H, dd, J 9, J′ 2.4, 5′-H), 6.39 (3H, m, 3′-H), 6.71 (6H, d, J 1,2″, 6″-H), 6.86 (3H, s, 4″-H), 7.01 (12H, d, J 1.7, 2′″, 6′″-H), 7.27(6H, m, 4′″-H), 7.30 (3H, d, J 1.7, 3-H), 7.43 (3H, dd, 4-H), 8.20 (3H,dd, 6-H); m/z (MALDI) 2373 (M⁺, 100%).

1. A process for modifying at least one dendron intended to form part ofa dendrimer, said dendron having the formula:FO(dendrite−Q_(a))_(y) wherein FO is a functional group attached, eitherdirectly or via a linking group which can contain one or more reactableunsaturated units, to the first branching atom or group of the dendrite,each “dendrite” which may be the same or different is a dendrite whichcontains branching atoms or groups and optionally linking groups andcomprises at least said first branching atom or group which must have,in addition to FO, 2 or more groups attached and in which the distalgroup of each arm of the dendrite is an aryl or heteroaryl group, atleast one of said dendrite or, if present, the linking group to FOcontaining one or more reactable unsaturated units, y is 1 or more, Q isa surface group and a is 0 or an integer, which comprises reacting atleast one said reactable unsaturated group in a chemoselective manner toform a less unsaturated group, with the proviso that the process doesnot comprise hydrogenating a dendron of the formula

where R is 2-ethylhexyloxy.
 2. A process for modifying a dendrimer ofthe formula:CORE−[dendrite−Q_(a)]_(x) wherein Q and a are as defined above, x is oneor 2 or more such that when x is more than one each dendrite−Qa can bethe same or different and CORE represents an atom or group and COREterminates at the single bond to the first branching atom or group inthe or each “dendrite”, each “dendrite” which may be the same ordifferent and is a dendrite which contains branching atoms or groups andoptionally linking groups, at least one of CORE and dendrite comprisingat least one reactable unsaturated group, provided that the distal groupof each arm of the or each dendrite is an aryl or heteroaryl group,which comprises reacting at least one reactable unsaturated group toform a less unsaturated group in a chemoselective manner.
 3. A processaccording to claim 2 wherein the reactable unsaturated group becomesfully saturated.
 4. A process according to claim 2 wherein only linkinggroups are reacted.
 5. A process according to claim 2 wherein thereactable unsaturated group is a vinylene or acetylenyl group.
 6. Aprocess according to claim 2 where the first branching point in thedendrite is a (hetero)aryl group or fused (hetero)aryl group.
 7. Aprocess according to claim 6 wherein all the branching points in thedendrite are aryl, heteroaryl or fused (hetero) aryl.
 8. A processaccording to claim 2 wherein the first branching point in the dendriteis a 1,3,5-substituted phenyl group or a 3,6-N-substituted carbazolegroup.
 9. A process according to claim 2 wherein the reactableunsaturated group is part of the core and directly bonded to the firstbranching group of a dendrite.
 10. A process according to claim 2wherein the dendrimer is asymmetric.
 11. A process according to claim 2wherein the dendrimer is an organometallic dendrimer.
 12. A processaccording to claim 2 wherein the group which has been reacted by achemoselective reaction is subsequently reacted further.
 13. A processaccording to claim 2 wherein the chemoselective reaction is an additionreaction.
 14. A process according to claim 2 wherein the chemoselectivereaction is a hydrogenation.
 15. A process according to claim 2 whereinthe chemoselective reaction involves hydrohalogenation, halogenation,hydrosilylation or hydroboration followed by oxidation.
 16. A processaccording to claim 2 wherein the chemoselective reaction is acycloaddition.
 17. A process according to claim 2 wherein the saidreactable unsaturated group is part of a dendrimer that has one at leastinherently partially conjugated dendrite.
 18. A process according toclaim 2 wherein the said reactable unsaturated group is part of adendrimer that comprises more than one at least inherently conjugateddendrite and the dendrites are attached to at least two ligandscomplexed to the metal cation which forms part of the core and thechemoselective reaction takes place in the core.
 19. A process accordingto claim 2 wherein the dendrimer has one or more surface groups whichallows patterning.
 20. A process according to claim 2 wherein the filmis capable of emitting visible light.
 21. A process for making adendrimer which involves reacting at least one dendron with a dendrimerprecursor wherein the dendron is one which has been modified by aprocess as claimed in claim
 1. 22. A dendron or dendrimer wheneverobtained by a process as claimed in claim
 2. 23. An organic lightemitting device comprising, in sequence, layers of a substrate, anelectrode, a first optional charge-transporting layer, a light emissivelayer, a second optional charge-transporting layer and a counterelectrode, wherein at least one of the emissive layer, first optionalcharge-transporting layer and second optional charge-transporting layersis a film of a dendrimer as claimed in claim
 22. 24. A device accordingto claim 23 wherein the emissive layer is a film of a dendrimer.
 25. Adevice according to claim 24 which comprises at least onecharge-transporting layer.
 26. A dendrimer of claim 22 in a photovoltaicdevice.